The effect of maternal position on placental blood flow and fetoplacental oxygenation in late gestation fetal growth restriction: a magnetic resonance imaging study

Abstract

Fetal growth restriction (FGR) and maternal supine going‐to‐sleep position are both risk factors for late stillbirth. This study aimed to use magnetic resonance imaging (MRI) to quantify the effect of maternal supine position on maternal‐placental and fetoplacental blood flow, placental oxygen transfer and fetal oxygenation in FGR and healthy pregnancies. Twelve women with FGR and 27 women with healthy pregnancies at 34–38 weeks’ gestation underwent MRI in both left lateral and supine positions. Phase‐contrast MRI and a functional MRI technique (DECIDE) were used to measure blood flow in the maternal internal iliac arteries (IIAs) and umbilical vein (UV), placental oxygen transfer (placental flux), fetal oxygen saturation (FO2), and fetal oxygen delivery (delivery flux). The presence of FGR, compared to healthy pregnancies, was associated with a 7.8% lower FO2 (P = 0.02), reduced placental flux, and reduced delivery flux. Maternal supine positioning caused a 3.8% reduction in FO2 (P = 0.001), and significant reductions in total IIA flow, placental flux, UV flow and delivery flux compared to maternal left lateral position. The effect of maternal supine position on fetal oxygen delivery was independent of FGR pregnancy, meaning that supine positioning has an additive effect of reducing fetal oxygenation further in women with FGR, compared to women with appropriately grown for age pregnancies. Meanwhile, the effect of maternal supine positioning on placental oxygen transfer was not independent of the effect of FGR. Therefore, growth‐restricted fetuses, which are chronically hypoxaemic, experience a relatively greater decline in oxygen transfer when mothers lie supine in late gestation compared to appropriately growing fetuses. imageKey points Fetal growth restriction (FGR) is the most common risk factor associated with stillbirth, and early recognition and timely delivery is vital to reduce this risk. Maternal supine going‐to‐sleep position is found to increase the risk of late stillbirth but when combined with having a FGR pregnancy, maternal supine position leads to 15 times greater odds of stillbirth compared to supine sleeping with appropriately grown for age (AGA) pregnancies. Using MRI, this study quantifies the chronic hypoxaemia experienced by growth‐restricted fetuses due to 13.5% lower placental oxygen transfer and 26% lower fetal oxygen delivery compared to AGA fetuses. With maternal supine positioning, there is a 23% reduction in maternal‐placental blood flow and a further 14% reduction in fetal oxygen delivery for both FGR and AGA pregnancies, but this effect is proportionally greater for growth‐restricted fetuses. This knowledge emphasises the importance of avoiding supine positioning in late pregnancy, particularly for vulnerable FGR pregnancies.

Magnetic resonance imaging of placental intralobule structure and function in a preclinical nonhuman primate model

“…Furthermore, our work with T2 * has already demonstrated high discriminatory power in prospectively identifying human pregnancies at risk of adverse pregnancy outcomes, such as pre-eclampsia and small gestational age [ 26 ]. Recent human studies using the combination of IVIM-DWI and T2/T2 * have provided a physiological explanation for the known causative link between maternal supine sleeping and late gestation stillbirth, whereby supine position has an additive effect on the reduced fetal oxygen supply seen in FGR compared with normal pregnancies, rendering fetal oxygen supply even more insufficient [ 27 , 48 ]. These studies support the generation of a validated quantitative model for joint IVIM-DWI and T2/T2 * relaxometry, which could significantly improve assessments of perfusion and potentially characterize fetal oxygen saturation in vivo.…”

DECIDE to sleep on your side: novel MRI approach unmasks phenomena relevant to stillbirth

“…examined maternal and fetal blood flows, and placental oxygen flux in the supine vs . LLD position at ∼36 weeks gestational age (Jani et al 2023). This is on the downwards curve of fetal growth velocity, when stillbirth risk for an already compromised fetus would be greatest (Figure).…”

Exploring the impact of maternal supine position on placental perfusion in late gestation fetal growth restriction by magnetic resonance imaging

“…However, little is known about the effect of the supine position on oxygen supply, and maternal-placental and fetoplacental blood flow in growth-restricted fetuses. This journal club's focus article by Jani et al (2023) combined novel non-invasive functional magnetic resonance imaging (MRI) techniques known as diffusion-relaxation combined imaging for detailed placental evaluation (DECIDE) to assess placental function, and phase-contrast MRI (PC-MRI) to quantitatively estimate and compare uteroplacental blood flow in appropriate gestation age (AGA) and FGR pregnancies. Furthermore, they aimed to study the effect on AGA and FGR pregnancies of a maternal supine position compared with the LLD position.…”

“…FGR can arise due to abnormalities during placental villous development, such as trophoblastic invasion into the maternal spiral arterioles. Limited oxygen reserved is preferentially redistributed to vital organs such as the brain and heart to compensate for the diminished placental resources at the expense of fetal growth, leading to fetal physiological complications (Jani et al., 2023). Ongoing or repetitive fetal hypoxaemic stress may eventually lead to fetal death due to fetal acidaemia.…”